The present invention relates broadly to enclosures, such as cases, cabinets, housings, or parts thereof such as doors or covers, for mobile, i.e., cellular telephone handsets and other electronic devices, and particularly to the manufacture of such enclosures as having a metallic conformal coating which may be used as a heat spreader.
Engineers involved in the design of portable and other electronic systems and devices, such as televisions, radios, computers, mobile, i.e., cellular telephone handsets, medical instruments, business machines, communications equipment, and the like, often face performance problems, as well as government and industrial regulations, concerning electromagnetic interference (EMI). As plastic-housed electronics continue to shrink in size and to run at higher clock speeds, the chances for EMI problems increase. Radio frequency (RF) and digital components, current carrying traces, wires, and other conductors are the typical sources of most EMI emissions. In some cases, the more “noisy” components can be moved away from sensitive areas. However, smaller devices and tightly packed boards minimize that opportunity in a great many systems.
Ultimately, most high-frequency systems require some form of EMI shielding at the enclosure level. These enclosures, which may be a case, cabinet, or housing, or a part thereof such as a door or cover, may be formed of a metal such as steel, aluminum, or magnesium, or alternatively, of a plastic or other polymeric material. While a metal housing is inherently an effective EMI barrier, plastic enclosure parts must be made electrically conductive in order to function as an EMI shield. This has typically been achieved by a conductive layer, such as a paint, metal-filled elastomer, or a metal foil or coating, which may be provided by fastening, laminating, lining, transferring, over-molding, spraying, dipping, cladding, plating, or metallizing, or otherwise which may be applied or deposited across the interior or exterior surfaces of the housing. Although each method may offer certain advantages to the designer, there is almost always a cost-performance tradeoff necessary in the selection. Such methods are further described in commonly-assigned of U.S. application Ser. No. 10/137,229, in commonly-assigned U.S. Pat. No. 5,566,055, in DE 19728839, U.S. Pat. Nos. 5,847,317; 5,811,050; 5,442,153; 5,180,639; 5,170,009; 5,150,282; 5,047,260; 4,714,623; and WO 00/29635; 99/43191; 99/40769; 98/54942; 98/47340; 97/26782, and in the following publications of the Chomerics Division of Parker Hannifin Corporation (Woburn, Mass.): “CHO-SHIELD® Conductive Compounds;” “CHO-SHIELD® EMI Shielding Covers,” Technical Bulletin 22, (1996); “CHO-VER SHIELD™ EMI Shielding Plastic Cover with Molded Conductive Elastomeric Gasket,” (1999); “CHO-SHIELD® 2052 Conductive Coating,” Technical Bulletin 48, (2000); “CHO-SHIELD® 2054 Conductive Coating,” Preliminary Product Data Sheet, (2000); “CHO-SHIELD® 2056 High Performance Conductive Coating,” Preliminary Product Data Sheet; and Ecoplate™ Metallic Conformal Coating Process. The best of these methods will accommodate the deepest recesses in a plastic housing part, where the smallest discontinuity may provide a pathway for spurious emissions.
Managing heat also can be crucial to maintaining the reliability and extending the life of portable and other electronic devices. Numerous cooling solutions, including heat sinks, heat pipes and flexible metal or ceramic heat spreaders, are available for shunting away excess component heat. These solutions typically require a separate heat sink or spreader attached to the heat-generating components. For certain applications, however, a more preferred solution would eliminate the need for such separate heat sinks or spreader.